The invention relates to a fluidised bed reactor for biological purification of effluent having carrier particles for biocatalysts, gassing units and having a retention system for the carrier particles.
In the purification of effluent, carrier particles for the microorganisms are used to an increasing extent in order to increase activity. Reactors used are fixed bed reactors and fluidised bed reactors. In fixed bed reactors, only a part of the reactor space is used due to uneven fouling which is adjusted naturally. In addition, constant process conditions (such as, for example pH value) are not maintained in the fixed bed. When concentration varies in the feed, the buffer effect of submersed biological life is not fully utilised due to lack of thorough mixing.
Well mixed fluidised bed reactors, in which the carriers for the microorganisms are suspended or are temporarily suspended, are therefore more suitable for the purification of effluent. Fluidisation is achieved by means of pumping liquid, by means of stirrers or by means of gassing the liquid. The disadvantage in pumping or stirring the liquid is that the effluent and the carrier particles can come into contact with the drive units. The carrier particles are thus subjected to intensive mechanical load which can lead in the long term to its destruction. To prevent this, additional screens must be installed to retain the solids.
In anaerobic purification of effluent, there is the further problem that the carrier particles have a tendency to float as a result of the floating effect of small bubbles of biogas which adhere to the solid. The solid layer which then forms on the surface of the liquid, as a rule, can no longer be recirculated by pumping or by the conventional stirring systems. On the other hand, when gassing the liquid, the microbubbles which adhere to the solid cause coalescence with the larger gas bubbles produced on gassing, so that floating of the solids can be avoided.